Preheat the oven to 350 degrees F (175 degrees C). Slice the tops off of the garlic bulbs so that the tip of each clove is exposed. Place the bulbs on a baking sheet, and drizzle with olive oil. Bake for 30 minutes, or until garlic is soft. Set the oven to broil. Slice the loaf of bread in half horizontally, and place cut side up on a baking sheet. Squeeze the cloves of garlic from their skins into a medium bowl. Stir in the butter, parsley, and Parmesan cheese until well blended. Spread onto the cut sides of the bread. Broil for about 5 minutes, until toasted.